Flexible printed wiring board for chip-on flexibles

ABSTRACT

There is provided a flexible printed wiring board including an insulating layer having a high optical transmittance, a high adhesion strength and a high migration resistance, and suitable for a chip on film (hereafter referred to as COF). In a flexible printed wiring board for COF, having an insulating layer on which a conductive layer of an electrodeposited copper foil is laminated, and an optical transmittance of 50% or more of the insulating layer in the etched region when a circuit is formed by etching said conductive layer, electrodeposited copper foil was made to have a rust-proofing layer of a nickel-zinc alloy on the adhering surface to be adhered to the insulating layer; the surface roughness (Rz) of the adhering surface was made to be 0.05 to 1.5 μm, and the specular gloss was made to be 250 or more when the incident angle is 60°.

CROSS REFERENCE TO RELATED APPLICATION

This application is a 35 USC § 371 National Phase Entry Application fromPCT/JP03/05891, filed May 12, 2003, and designating the U.S.

TECHNICAL FIELD

The present invention relates to a flexible printed wiring board, andspecifically to a flexible printed wiring board suitable for achip-on-film type.

BACKGROUND ART

In recent years, accompanying the progress of the electronic deviceindustry, demands for flexible printed wiring boards for mountingelectronic parts such as ICs and LSIs have rapidly increased. Thus, thedown sizing, that is, the size and weight reduction, and functionalenhancement of electronic devices themselves have markedly progressed.For this purpose, packaging systems using flexible film carrier tapes,such as TAB (tape automated bonding) tapes, T-BGA (ball grid array)tapes, and ASIC (application specific integrated circuit) tapes, havebeen adopted. Particularly, in electronic devices having Liquid crystaldisplays, such as personal computers and mobile telephones, the progresstoward high precision and thickness reduction is sharp, and flexibleprinted wiring boards having fine-pitch circuits formed thereon, whichhas not been realized conventionally, have been demanded; furthermore,there is an urgent need for the establishment of a method for mountingICs and the like thereon.

In order to satisfy the demand for downsizing of electronic devices asdescribed above, the technique for enabling ICs and the like to bemounted in narrow spaces is required. The techniques recently attractingattention include a packaging system known as chip on film (hereafterabbreviated as COF). In COF, a laminate of a copper foil (conductivelayer), which is a conductive material forming a conductive circuit, anda film consisting of an insulating material such as polyimide(insulating layer)) is used; and the laminated film (hereafter referredto as flexible laminated board) is subjected to etching treatment toform a conductive circuit to be a flexible printed wiring board, whereonIC chips are directly mounted to perform packaging (COF).

A flexible printed wiring board used in the COF has no device holes asin a conventional TAB tape, and no inner leads corresponding to theconductive circuit portion not supported by the film exist. Namely,since the conductive circuit (even if it is an inner lead) is always inthe state supported by the film, the line space of the conductivecircuit corresponding to the inner lead of the TAB tape can be madefurther finer. The reason is that since the film is supported, thestrength of the conductive circuit required during bonding can besecured even if the conductive circuit is made finer.

Since the flexible printed wiring board for COF has no device holes, thealignment in mounting IC or the like is performed by radiating lightonto the conductive circuit pattern from one direction, confirming thetransmitted light of the film on the opposite side, and directlyrecognizing the conductive circuit pattern shape. Since the alignmentmethod using transmitted light can be applied to conventionally employedmounting machines for TAB tapes, the use of expensive equipment such asa chip bonder exclusively used in COF is not required, and the methodtends to be widely adopted. For these reasons, a flexible printed wiringboard for COF is required to have optical transmittance of the degree toexactly recognize alignment patterns.

As a flexible printed wiring board used for COF, a two-layer type boardis known as obtained using a method wherein a seed layer of a metal suchas nickel is formed on the surface of the film of a polyimide resin orthe like (insulating layer), and copper to be a conductor is plated onthe metal seed layer. In the flexible printed wiring board obtainedusing this method, known as a direct metallization method, since theinsulating layer constituted by a polyimide resin or the like is formedin a relatively transparent state and has a high light transmittance,alignment for IC mounting can easily be performed; however, it has beenpointed out that the adhesion between the formed conductor circuit andthe insulating layer (peel strength) is low, and tends to causemigration.

In addition, it has been known that other flexible printed wiring boardscan be manufactured using a casting method wherein a polyimide resin orthe like as an insulating layer is applied to the surface of a conductorsuch as copper foil; or the most popular lamination method wherein acopper foil is bonded on such a film as a polyimide resin as theconductive layer for forming the conductive circuit. The flexibleprinted wiring board obtained using these casting method or laminationmethod excels in adhesion between the insulating layer and theconductive layer, and has high migration resistance compared with thedirect metallization method. However, since the insulating layer on theportion from which the copper foil, i.e., the conductive layer, wasetched off became the replica of the adhering surface of the copperfoil, it tended to scatter light, and there might be the case wherealignment using transmitted light could not be performed in IC mounting.

Therefore, it is the current status that when a flexible printed wiringboard produced by the casting method or lamination method is used forCOF, alignment holes must be separately formed in the insulating layersuch as a polyimide resin by laser processing or the like in addition tothe etching treatment for forming the conductive circuit.

To solve such problems, the present applicant has proposed a laminatedfilm and a film carrier tape suitable for COF applications (e.g., referto Patent Reference 1, Japanese Patent Laid-Open No.2003-23046). Thislaminated film has a structure wherein a conductive layer and aninsulating layer are laminated, and is characterized in that the opticaltransmittance of the insulating layer in the region from which theconductive layer has been etched off is 50% or more. In addition, thecopper foil for forming the conductive layer has produced a laminatedfilm having a high optical transmittance by setting the surfaceroughness of the adhering surface thereof at 0.1 to 1.8 μm. Such alaminated film and film carrier tape can perform a good alignment inmounting ICs and the like.

However, when a copper foil having a reduced surface roughness of theadhering surface is used, the adhesion between the conductive layer andthe insulating layer, that is, the lowering of the peel strength of theconductive circuit, cannot be avoided, and the laminated film having adesired peel strength must be manufactured after various examinations,such as the type of the resin constituting the insulating layer, and thesurface treatment method including surface roughness on the adheringsurface of the copper foil. Although the optical transmittance of thelaminated film can be controlled to some extent by controlling thesurface roughness on the adhering surface of the copper foil, it is thepresent situation that there are no findings on parameters for qualitycontrol of the adhering surface of the electrodeposited copper foil inorder to realize the laminated film having a predetermined opticaltransmittance and a good adhesion, and the early clarification isrequired.

The present invention is devised in the above-described situations, andthe object of the present invention is to provide a flexible printedwiring board suitable for COF that realizes a high optical transmittanceof the insulating layer on the constitution of the flexible printedwiring board, and excels in the adhesion between the conductive layerand the insulating layer, and migration resistance.

DISCLOSURE OF THE INVENTION

As described above, when a conductive layer is laid on an insulatinglayer by the casting method or the lamination method, and etching isperformed for forming a conductive circuit, the surface shape of theportion of the insulating layer from which an electrodeposited copperfoil, which is a conductive layer, was etched off becomes, the replicaof the adhering surface of the copper foil. In other words, if thesurface of the copper foil adhered to the insulating layer is flat, thesurface of the film, which is the replica thereof, is also in a flatstate. However, on the contrary, a reciprocal action to lower theadhesion strength occurs. Therefore, the present inventors devotedthemselves in the examinations on the characteristics of the adheringsurfaces of electrodeposited copper foils, that is, the surfaceroughness and the rust proofing treatment thereof, and the opticaltransmittance and the adhesion strength of the insulating layerconstituting a flexible printed wiring board, and devised the presentinvention.

The present invention is a flexible printed wiring board for COF, havingan insulating layer on which a conductive layer of an electrodepositedcopper foil is laminated, and an optical transmittance of the insulatinglayer in the etched region when a circuit is formed by etching theconductive layers of 50% or more, characterized in that theelectrodeposited copper foil includes a rust-proofing layer of anickel-zinc alloy on the adhering surface to be adhered to theinsulating layer; and the surface roughness (Rz) of the adhering surfaceis 0.05 to 1.5 μm, and the specular gloss when the incident angle is 60°is 250 or more.

In most cases, the surface shape of an electrodeposited copper foil isspecified using the surface roughness value thereof, and in general, ifthe surface roughness value is small, the surface is flat, and the largevalue is used to indicate a rough surface. Although the surfaceroughness value is important as a parameter to indicate the surfaceshape, it is the average of values representing the irregularity on thesurface shape. Therefore, it could not be said to be sufficient toidentify the surface shape affecting the scattering of light. In otherwords, even if the measured value of surface roughness was small, therewas an insulating layer that became the surface state having not so highoptical transmittance. Therefore, the present inventors measured thespecular gloss of the adhering surfaces of copper foils to identify thesurface shape, and found that the specular gloss of the adheringsurfaces had correlation with the optical transmittance of theinsulating layer after etching.

Furthermore, the present inventors conducted various examinations on thesurface treatments thereof, particularly on rust proofing treatment, inorder to make adhesion with the insulating layer excellent even if theroughness is very low as in the electrodeposited copper foil used in theflexible printed wiring board of the present invention, and made theadhering surface of the electrodeposited copper foil be provided with arust proofing layer of a nickel-zinc alloy.

The flexible printed wiring board according to the present invention hasthe optical transmittance of the insulating layer after the etchingtreatment of the conductive layer is 50% or more, and the adhesionstrength between the formed conductive circuit and the insulating layerhas practically no problem. Thus, the formation of a very fine conductorthat excels in migration resistance is enabled.

Although it cannot be said that distinct standards exist for the opticaltransmittance of flexible printed wiring boards for COF, from theconventional experiences, the transmittance is measured by transmittingvisible light, that is light having a wavelength of 400 to 800 nm or soas a light source. Since some materials of the insulating layer, that isthe film significantly absorbs the wavelength of 500 nm or below,generally, the light source of the wavelength range between 600 and 700nm is used. This wavelength range is a light source used in the imageprocessing by a so-called CCD camera or the like, and it is consideredthat if the optical transmittance in this wavelength range is about 50%or. more, alignment can be easily and surely performed. In other words,the flexible printed wiring board according to the present invention canmake the optical transmittance of the insulating layer after etching theelectrodeposited copper foil 50% or more in a range of wavelengthsbetween 600 and 700 nm, even if there is some difference in the materialor the like of the insulating layer, and therefore alignment in mountingICs can be surely performed.

In the case of a flexible printed wiring board that can realize such ahigh optical transmittance, it is required to make the surface roughnessof the adhering surface of the electrodeposited copper foil Rz 0.05 to1.5 μm, and make the specular gloss (incident angle: 60°) 250 or more.As described above, even if the surface roughness is small to someextent, there may be the case where a practical optical transmittancecannot be secured. Therefore, based on the results of the presentinventors' examinations, it was concluded that the surface roughness ofthe adhering surface of the electrodeposited copper foil was 1.5 μm orbelow in Rz, and the specular gloss at an incident angle of 60° was 250or more. Although the flexible printed wiring board of the presentinvention can be constituted even if the surface roughness Rz is lessthan 0.05 μm, considering the difficulty of manufacturing anelectrodeposited copper foil having an ultra-low roughness of less thanRz 0.05 μm, this lower limit was determined. This difficulty is aproblem in the manufacturing technique, for example, in manufacturing anelectrodeposited copper foil of ultra-low roughness, since the surfaceof the rotating drum cathode used for manufacturing thereof is madeextremely smooth, the electrodeposited copper foil deposited on thecathode in the electrolyte solution is easily detached from the cathodesurface, and the detached electrodeposited copper foil contacts theanode to make a short circuit.

It is also desired that the specular gloss of the adhering surface ofthe electrodeposited copper foil of the flexible printed wiring boardaccording to the present invention at an incident angle of 20° is 100 ormore. Since the specular gloss at an incident angle of 60° is the valuemost widely used as the measurement range of a gloss meter, it wasadopted. Furthermore, the present inventors examined the specular glossfor various incident angles in accordance with JIS Standards (JIS Z8741), and decided that the high optical transmittance, which is theobject of the present invention, could be realized when the speculargloss is 100 or more, as a result of the measurement of the adheringsurface of the electrodeposited copper foil at an incident angle of 20°in the case of a high specular gloss (specular gloss is 70 or more at anincident angle of 60°).

Furthermore, in order to provide the electrodeposited copper foil forthe flexible printed wiring board according to the present inventionwith a good adhesion while realizing a high optical transmittance, arust proofing layer of a nickel-zinc alloy is formed on the surfacewhere the electrodeposited copper foil attaches without performingnodular treatment. The nickel-zinc alloy in this case has preferably thecomposition of 50 to 99 wt % nickel and 50 to 1 wt % zinc. This rustproofing layer plays a role of preventing the surface oxidation of theelectrodeposited copper foil itself, as well as improving the adhesionstrength between the adhering surface and the insulating layer, andmigration resistance properties. In a flexible printed wiring board forCOF, polyimide, polyester, polyamide, polyether sulfone, liquid-crystalpolymers and the like are used as insulating material, and all aromaticpolyimide is most preferable. The nickel-zinc alloy is effective forimproving adhesion to these insulating materials. Especially, nickeltends to improve the adhesion to polyimide-based insulating materials.If the content of nickel is less than 50 wt %, the improvement ofadhesion cannot be secured, and if the content of nickel exceed 99 wt %,nickel remains easily when etching treatment is performed. If thecontent of zinc is less than 1%, copper tends to diffuse into theinsulating layer side due to thermal history produced in manufacturingthe flexible printed wiring board (by the casting method or thelamination method), and as a result, the adhesion strength cannot besecured. If the content of zinc exceeds 50%, corrosion resistance to anSn plating solution used in the manufacture of the flexible printedwiring board, and detachment of the conductive circuit tends to occur.

In the rust proofing treatment of the electrodeposited copper foil ofthe flexible printed wiring board according to the present invention, itis practically preferable that the quantity of the nickel-zinc alloyapplied to the adhering surface is 20 to 100 mg/m². If the quantity isless than 20 mg/m², the adhesion strength cannot be secured, and if thequantity exceeds 100 mg/m², there is the tendency of causing etchingresidue during etching for forming the conductive circuit. Furthermore,when the rust proofing treatment is performed using this nickel-zincalloy, the quantity ratio of nickel and zinc is preferably within arange between 4:1 and 7:3. If the proportion of nickel in thenickel-zinc alloy exceeds 80%, etching residue tends to occur. If theproportion of zinc exceeds 30%, the adhesion strength tends to lower.

The rust proofing layer is composed of a nickel-zinc alloy layer whereona chromate layer is formed, and it is preferable to form a silanecoupling agent adsorbed layer whereon an amino functional silanecoupling agent is adsorbed is formed on the surface of the rust proofinglayer. The chromate layer and the silane coupling agent adsorbed layerfurther improve the adhesion to the insulating layer, and can alsoimprove moisture resistance and chemical resistance.

The kind of the silane coupling agents is not limited, and for example,vinyltrimethoxysilane, vinylphenyltrimethoxysilane,γ-methacryloxypropyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane,4-glycidylbutyltrimethoxysilane, imidazolsilane, triazinesilane, andγ-mercaptopropyltriiethoxysilane can be used. Also according to thepresent inventors' examinations, amino-functional silanes are confirmedto be especially preferable in polyimide-based insulating materials. Forexample, amino-functional silanes include γ-aminopropyltriethoxysilane,N-β(aminoethyl)γ-aminopropyltrimethoxysilane, andN-3-(4-(3-aminopropoxy)butoxy)propyl-3-aminopropyltrimethoxysilane.

As described above, in the flexible printed wiring board according tothe present invention, although a polyimide-based resin is often used asthe insulating layer, the adhesion between the insulating layer composedof such a polyimide-based resin and the electrodeposited copper foil isnot so good, and it is said that the adhesion strength (peelingstrength) is difficult to secure. In particular, when anelectrodeposited copper foil is directly adhered to a film or a basematerial consisting of a polyimide-based resin without using an adhesiveor the like, the adhesion is much worsened. However, when the rustproofing layer is formed of a nickel-zinc alloy, and an amino functionalsilane coupling agent adsorbed layer is further formed, the adhesionstrength to the insulating layer consisting of a polyimide-based resincan be maintained at a certain level.

When a resin agent is applied, for example, as a cast solution on thesurface of an electrodeposited copper foil to form an insulating layerof a polyimide-based resin, the use of the above-describedamino-functional silane as silane coupling agent can further improve theadhesion. The present inventors may explain the result as follows:Captone, a typical polyimide, forms polyamic acid through the reactionof an acid anhydride with a diamine, and dehydration between the NHgroup and the OH radical of the COOH group in the polyamic acid closesthe imide ring to form eventually polyimide. Here, it is considered thatin the flexible printed wiring board according to the present invention,when the adhering surface of the electrodeposited copper foil has theamino functional silane, the OH of the polyamic acid chemically bonds toH of the hydrolysis product of the amino functional silane through adehydration reaction, and excellent adhesion strength is realized.

In the flexible printed wiring board according to the present inventionas described above, it is preferable to use the shiny side of theelectrodeposited copper foil as the adhering surface thereof. Accordingto the present inventors' examinations, it was confirmed that theoptical transmittance of the insulating layer lowered even if theadhering surface had a surface roughness value of less than Rz 2 μm. Theflexible printed wiring board of the present invention is formed usingan electrodeposited copper foil, and the electrodeposited copper foil isnormally manufactured by immersing a-rotating drum cathode in a coppersulfate electrolytic solution to electrodeposit copper on the peripheralsurface of the rotating drum cathode through the electrolysis reaction,and continuously peeling the electrodeposited copper from the peripheralsurface. In this electrodeposited copper foil, the surface of the sideof initial electrodeposition, that is, the side whereonelectrodeposition onto the peripheral surface of the rotating drumcathode started, is called the shiny side; and the opposite electrolysiscompleting side is called the matte side for distinguishing. In otherwords, the shiny side is the flat surface to be the transferring shapeof the electrodeposited surface of the rotating drum cathode; and thematte side is the “delustered” surface having irregularity. A copperfoil called an LP foil (low profile copper foil) is an electrodepositedcopper foil controlled to have a considerably low surface roughnessvalue on the matte side, and the matte side has usually little gloss. Inthus obtained electrodeposited copper foil, considering the adhesionstrength to prepreg or the like composing so-called rigid printed wiringboard, a roughened treatment called nodular treatment is generallyperformed on the matte side that becomes the adhering surface to theprepreg. When such a roughened treatment is performed, the glossiness ofthe surface thereof further lowers, and naturally, when the surface ofsuch a low glossiness is used as the adhering surface, the opticaltransmittance of the insulating layer is almost always worsened.

Therefore, the present inventors have tested a number of methods formanufacturing an electrodeposited copper foil used in the flexibleprinted wiring board according to the present invention, and have foundthat the following manufacturing method is preferred: As the method formanufacturing an electrodeposited copper foil used in the flexibleprinted wiring board according to the present invention, the peripheralsurface of a rotating drum cathode is polished until it has a surfaceroughness of 0.05 to 1.5 μm (Rz); the rotating drum cathode is immersedin a copper sulfate electrolytic solution to electrodeposit copper onthe peripheral surface of a rotating drum cathode; the electrodepositedcopper is continuously peeled off the peripheral surface to form theelectrodeposited copper foil; and the above-described rust proofinglayer and silane coupling agent adsorbed layer is appropriately formedthe shiny side of the electrodeposited copper foil.

As described above, since the shiny side of the electrodeposited copperfoil becomes the replica of the peripheral surface of a rotating drumcathode, polishing is performed until the surface roughness becomes 0.05to 1.5 μm (Rz). By appropriately forming a nickel-zinc alloy layer, achromate layer, and a silane coupling agent adsorbed layer on the shinyside of the electrodeposited copper foil obtained from the rotating drumcathode subjected to such polishing treatment, the copper foil for theflexible for the printed wiring board of the present invention can bemanufactured. In this case, polishing the surface of the rotating drumcathode will easily produce polishing streaks along the circumferentialdirection thereof, and it is desired to allow as few polishing streaksas possible to be produced. This is because if the polishing streaksoutstand, the specular gloss of the shiny side may be lowered in theobtained electrodeposited copper foil even if the surface roughnessvalue of the peripheral surface is 0.05 to 1.5 μm (Rz). In other words,this is because specular gloss values tend to differ between the lengthdirection (MD direction) and the drum width direction (TD direction) inthe obtained electrodeposited copper foil.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially enlarged perspective view of a metal foilelectrodepositing apparatus;

FIG. 2 is photographs of the adhering surface of the copper foil ofExample 1 observed using an SEM; and

FIG. 3 is a photograph showing the result of the laser microscopeobservation of the adhering surface of the copper foil of Example 1.

BEST MODE FOR CARRYING OUT THE INVENTION

Preferred embodiments of the present invention will be described below.

First Embodiment

First, in the first embodiment, the manufacture of an electrodepositedcopper foil used in the flexible printed wiring board of the presentinvention will be described. The electrodeposited copper foil ismanufactured with electrodeposited copper foil manufacturing equipmentusing a conventionally known rotating drum cathode, and the schematicsectional view is shown in FIG. 1. The electrodeposited copper foilmanufacturing equipment 1 is equipped with a rotating drum cathode 2made of titanium (diameter: 3 m; width: 1.35 m) for electrodepositingcopper, and an insoluble anode 3 known as DSA placed opposite along theperipheral surface shape of the rotating cathode 2. The rotating cathode2 and the anode 3 are connected to a power supply unit (not shown). Therotating drum cathode 2 is designed so that a substantially half of thevolume is immersed in an electrolyte solution; the anode 3 is dividedinto two portions, and an electrolyte supply means 5 having anelectrolyte supply port 4 for supplying an electrolyte from the bottomof the rotating cathode 2 is installed between the divided portions ofthe anode 3. When a copper sulfate electrolyte solution is supplied fromthe electrolyte supply port 4 toward the rotating cathode 2, as thebroken lines in FIG. 1 show, the electrolyte solution flows upwardlyalong the peripheral surface shape of the rotating cathode 2, andoverflows into an electrolysis vessel 7. The copper foil 6 deposited onthe peripheral surface of the rotating cathode 2 is pealed from therotating cathode. 2, and is wound around a take-up roll 9 past a guideroll 8. Table 1 shows the manufacturing conditions of theelectrodeposited copper foil.

TABLE 1 Copper concentration 82 g/L Sulfuric acid concentration Total300 g/L Current density 50 DK Electrolyte temperature 50° C. Chlorineconcentration 2 ppm

The peripheral surface of the rotating drum cathode made of titanium wassubjected to polishing treatment using PVA (polyvinyl acetal) grindstone, and after mounting on the above-described electrodeposited copperfoil manufacturing equipment, the peripheral surface was subjected tobuffing treatment using a #2500 buff using aluminum oxide as an abrasivecoating so that the surface roughness of the peripheral surface becamewithin a range between Rz 0.05 and 1.5 μm. Thereafter theelectrodeposited copper foil was manufactured under the conditions shownin Table 1. The electrodeposited copper foil used in this embodiment wasthe one called the VLP type (very low profile type, surface roughness ofthe matte side: Rz 1.5 to 5.0 μm), and was manufactured to have athickness of 12 μm.

Three lots of electrodeposited copper foils were prepared as describedabove; the shiny side thereof was subjected to rust-proofing consistingof nickel-zinc alloy plating treatment, chromate treatment and silanecoupling agent treatment in this order; and the electrodeposited copperfoils for flexible printed wiring boards of this embodiment weremanufactured. The surface treatments were conducted under the conditionsas shown in Table 2. These treatments were performed using s surfacetreating machine known to the art (not shown) that rewinds the rolledelectrodeposited copper foil from a direction, performs each surfacetreatment on the copper foils sequentially guided to each treatmentvessel by guide rolls, and finally performs a drying treatment and takesup the copper foils as rolls.

TABLE 2 Acid pickling Sulfuric acid 100 g/L pretreatment Nickel-zincPyrophosphoric acid bath Ni 0.3 g/L alloy plating Composition: Zn 2.5g/L 40° C. Electrolytic Chromic acid 1.0 g/L chromate treatment Silanecoupling γ-aminopropyltrimethoxysilane 5.0 g/L agent treatment

For the three lots of the electrodeposited copper foils, surfacetreatment was performed on the shiny side thereof under the conditionsshown in Table 2 to fabricate three lots of electrodeposited copperfoils for flexible printed wiring boards (Examples 1 to 3). Forcomparison, two lots of buff-polished copper foils proposed by thepresent applicant for ultra-fine patterns were also prepared(Comparative Examples 1 and 2). The buff-polished copper foil is acopper foil manufactured by physically polishing the matte side of anelectrodeposited copper foil to clear away the irregularity on the matteside, and performing nodular treatment, rust-proofing treatment(nickel-zinc plating and chromate treatment) and silane coupling agenttreatment onto the buff-polished matte side thereof (for details, referto Japanese Patent Laid-Open No. 9-195096). The buff-polished copperfoils of the Comparative Examples have been developed for applying toultra-fine patterns, and have been used as copper foils suitable toapplications such as rigid printed wiring boards and TAB tapes. Theelectrodeposited copper foils used in the Comparative Examples were of aVLP type manufactured under the above-described electrolysis conditions(except for the surface roughness of the peripheral surface of therotating drum cathode), and had a thickness of 15 μm after bufffinishing.

For Examples 1 to 3 and Comparative Examples 1 and 2, the results ofmeasuring the surface roughness of the adhering surface side thereof,and each quantity per unit area of rust proofing treatment will bedescribed. The surface roughness was calculated in accordance with JIS B0601, as the ten-point-average roughness (Rz). The quantity per unitarea of rust proofing treatment was measured by cutting a sample of apredetermined area, preparing solutions by dissolving the surface of thesample, and obtaining the concentration of Ni, Zn and the like in thesolution by measuring the absorption of light of the solution with ICPto calculate each quantity per unit area. Table 3 shows the results ofmeasurements.

TABLE 3 Specular gloss Adhering surface Incident Incident Roughness NiZn Cr angle 60° angle 20° Optical Rz quantity quantity quantity MD TD MDTD transmittance % Example 1 0.70 23 9 0.5 374 304 220 160 72 Example 20.59 25 10 0.5 404 337 330 230 65 Example 3 0.81 26 11 0.6 438 360 290260 80 Comparative 1.40 16 13 4.0 1.5 12.5 1.0 0.8 22 Example 1Comparative 1.80 18 15 4.0 1.0 5.0 1.4 0.9 35 Example 2 (Unit of Ni, Znand Cr quantities: g/m²)

Here, the results of measuring the specular gloss of the adheringsurface side, and the optical transmittance of each copper foil will bedescribed. The specular gloss was measured using a Handy Gloss meterPG-1M (manufactured by Nippon Denshoku Industries Co., Ltd.), and thevalues when the incident angles were 60° and 20° were adopted. Theoptical transmittance was measured using an absorptiometer, by applyinga commercially available polyimide varnish (Rikacoat SN-20 manufacturedby New Japan Chemical Co., Ltd.) to each copper foil and heated to forma laminated film formed by laminating polyimide insulating layers of athickness of 40 μm, partially removing the copper foil by etching thelaminated film, and radiating light to the removed area. The measuringwavelengths were 400 to 800 nm, and the optical transmittance when thewavelength was 600 nm was adopted as the representative value. Theresults are shown in Table 3.

The specular gloss was measured along two directions of theelectrodeposited copper foil produced: the direction corresponding tothe circumferential direction of the rotating drum cathode (MD), and thedirection corresponding to the width direction of the rotating drumcathode (TD). As a result, the adhering surfaces of Examples 1 to 3 wereconfirmed to have very high specular gloss values, and it was found thatthe optical transmittance was 50% or more, accordingly. On the otherhand, the specular gloss of comparative example 1 or 2 was a very smallvalue because the nodular treatment has been performed. In addition, theoptical transmittance was lower than 50%, and the optical transmittanceconsidered to be required for alignment could not be obtained. Here, forreference, the results of measuring the specular gloss on thenon-adhering surface of Comparative Examples 1 and 2 are shown in Table4.

TABLE 4 Non-adhering surface (specular gloss) Non-adhering Incidentangle 60° Incident angle 20° surface Roughness MD TD MD TD RzComparative 71 59 19 17 1.7 Example 1 Comparative 85 67 20 18 1.5Example 2

The non-adhering surface of Comparative Examples 1 and 2 shown in Table4 corresponds to the shiny side of an electrodeposited copper foil, andin the case of the electrodeposited copper foils of the ComparativeExamples, the surface roughness of the peripheral surface of therotating cathode on the manufacture of the electrodeposited copper foilswas about 1.5 to 2.0 μm, and some polishing streaks were observed.Although the decisive reason why the specular gloss of ComparativeExamples became so small values was unknown, it was estimated that thespecular gloss did not necessarily increase even if the surfaceroughness value was simply small.

Next, the results of observing the adhering surface of theelectrodeposited copper foil for flexible printed wiring boardsaccording to the first embodiment will be described. FIG. 2 showsphotographs of the adhering surface of the copper foil of Example 1observed using an SEM. FIG. 2( a) is a photograph of a magnification of100; and (b) is a photograph of a magnification of 2,000. As seen fromthese photographs, the adhering surface is very flat, and polishingstreaks are very small.

FIG. 3 shows a profile obtained by scanning the adhering surface of thecopper foil of Example 1 with a laser microscope. In FIG. 3, what whitelines show is the profile (×800) of the adhering surface obtained bylaser scanning in the TD direction of the copper foil. As seen fromthis, the adhering surface of Example 1 was confirmed that the surfaceroughness value was small, and the irregularity was very small andbecame nearly uniform.

Second Embodiment

In the second embodiment, the results of examinations about the speculargloss and the optical transmittance of the adhering surface of anelectrodeposited copper foil characterized by the types and the surfacetreatment thereof, particularly with or without nodular treatment, willbe described. Table 5 shows various electrodeposited copper foils, andthe results of the specular gloss and the optical transmittance thereof.

TABLE 5 Adhering surface Specular gloss Roughened Roughness Incidentangle 60° Optical Conductive layer treatment Rz μm MD TD transmittance %Comparative Normal foil matte Yes 4.5 1.3 1.1 1.1 Example A-1 surfaceComparative Matte side of low- Yes 3.5 1.0 1.0 0.8 Example A-2 roughnessfoil Comparative Shiny side of low- Yes 2.6 0.1 0.2 3.7 Example A-3roughness foil Comparative Shiny side of low- Yes 1.7 0.3 0.8 31.3Example A-4 roughness foil Comparative Shiny side of low- No 1.6 74.8100.6 44.9 Example A-5 roughness foil Comparative Vacuum-deposited +copper- No — — — 75.0 Example A-6 plated foil Example A-1 Foil of thepresent No 0.8 376.0 318.0 76.3 embodiment

Table 5 lists samples used for comparison as Comparative Examples A-1 to6. Specifically, the normal foil of Comparative Example A-1 meanselectrodeposited foil that falls under Grade III of JIS for copper foilshaving an irregular matte side whose convex portions have been subjectedto nodular treatment of tiny copper particles (thickness: 18 μm). Thelow-roughness foil of Comparative Example A-2 means an electrodepositedfoil referred to the VLP type (very low profile type, surface roughnessof matte side Rz: 1.5 to 5.0 μm) described in the first embodiment(thickness: 12 μm). However, the low-roughness foil used here wasmanufactured through a sequence of steps where the peripheral surface ofa rotating drum cathode made of titanium was polished using PVAgrindstone, and the cathode drum was mounted on the above-describedelectrodeposited foil manufacturing equipment, the peripheral surfacewas buff-polished with a #1500 buff using aluminum oxide as the abrasivecoating until the surface roughness of the peripheral surface turnedwithin a range between Rz 1.6 and 1.8 μm, and manufactured under theelectrolysis conditions described in Table 1. The low-roughness foilsubjected to nodular treatment on the matte side is Comparative ExampleA-2; and the ones subjected to nodular treatment on the shiny sides areComparative Examples A-3 and A-4. Here, the nodular treatment for A-1 toA-3 were performed under ordinary treatment conditions wherein afterperforming burnt plating, seal plating was performed as described below:

1. Conditions of burnt plating treatment Copper sulfate (copperconcentration) 10 g/L Sulfuric acid 170 g/L Liquid temperature 50° C.Treating time 2 seconds 2. Conditions of seal plating treatment Coppersulfate (copper concentration) A-1 50 g/L A-2 140 g/L A-3 50 g/LSulfuric acid 170 g/L Liquid temperature 50° C. Treating time 2 seconds

The nodular treatment for A-4 was performed by performing burnt platingtreatment using a burnt plating solution containing 1 g/L of arsenic(As) as an additive (other conditions were same as the above treatmentconditions), and then performing seal plating using the sameconcentration of a seal plating solution as in Comparative Example A-1(other conditions were same as the above treatment conditions). By thisnodular treatment for A-4, copper particles (0.1 to 1 μm), finer thancopper particles (1 to 2 μm) formed under ordinary nodular treatmentconditions, were electrodeposited as nodules.

Comparative Example A-5 was a low-roughness foil subjected to rustproofing treatment without performing nodular treatment on the shinyside of the low-roughness foil. Comparative Example A-6 was made by amethod known as direct metallization, wherein a Cr—Ni film (70angstroms) was formed by vapor deposition on a side of a polyimide film(Toray-DuPont Co., Ltd., Capton E N, thickness: 38 μm), and thevapor-deposited film was subjected to copper plating treatment to formcopper as a conductive layer (8 μm). Furthermore, Example A-1 wasExample 3 used in the above-described first embodiment. In addition, therust proofing treatment for Comparative Examples A-1 to 5 was the sameas the treatment for Example A-1 shown in Table 3. The opticaltransmittance of Comparative Examples A-1 to 5 and Example A-1 wasmeasured by applying a commercially available polyimide varnish(Rikacoat SN-20 manufactured by New Japan Chemical Co., Ltd.) to eachcopper foil and heated to produce a laminated film formed by laminatinga polyimide layer 40 μm thick as in the first embodiment. Since themeasurement of surface roughness and optical transmittance was the sameas in the above-described first embodiment, the description thereof willbe omitted.

As seen from Table 5, the samples subjected to nodular treatment on theadhering surfaces had large surface roughness values, and small speculargloss values (incident angle: 60°); accordingly, the opticaltransmittance was very low. In addition, even when the shiny side notsubjected to nodular treatment was used as the adhering surface, if thesurface roughness value became 1.6 μm, the specular gloss value at anincident angle of 60° was not so large, and as a result, the opticaltransmittance was not a practically satisfactory level. On the otherhand, in the case of Comparative Example A-6 prepared using the directmetallization method, since copper-plating treatment was performed onthe vapor-deposited film, the result of the measurement of opticaltransmittance was naturally high. In the case of Example A-1, thesurface roughness was as small as 0.8 μm, and the specular gloss(incident angle: 60°) was 300 or more; accordingly, it was known thatthe optical transmittance was high.

Third Embodiment

Finally, concerning the rust proofing treatment on the adhering surfaceof electrodeposited copper foils, the results of examining the adhesionand migration resistance when flexible printed wiring boards wereconstituted will be described.

Adhesion study in the third embodiment was conducted using theelectrodeposited copper foil prepared in the same manner as in Example 3of the above-described first embodiment, whereto each rust proofingtreatment shown in Table 6 was performed.

TABLE 6 Surface treatment of adhering surface Evaluation Rust proofingtreatment Pealing strength Adhering (kgf/cm) quantity Silane couplingagent In normal After Optical Kind mg/m² Type Concentration stateheating Blackening transmittance (%) Comparative Zn 36.3 a 5 0.38 0.27Good 73.1 Example B-1 Comparative Zn 36.3 b 5 0.24 — Good 68.4 ExampleB-2 Comparative Zn 36.3 c 5 0.00 — Good 69.2 Example B-3 Comparative Zn36.3 d 5 0.10 — Good 71.5 Example B-4 Comparative Zn 36.3 e 5 0.41 0.24Good 70.3 Example B-5 Comparative Sn 33.0 a 5 0.44 0.68 No good 51.5Example B-6 Comparative Sn 38.3 e 5 0.49 0.68 No good 48.7 Example B-7Comparative Ni 123.0 a 5 0.50 0.76 No good 46.3 Example B-8 ComparativeNi 118.8 e 5 0.52 0.65 No good 52.2 Example B-9 Comparative Co 117.6 a 50.56 0.70 Good 69.9 Example B-10 Comparative Co 108.2 e 5 0.48 0.59 Good69.5 Example B-11 Comparative Zn, 16.1 a 5 0.68 0.23 Good 71.9 ExampleB-12 Ni 6.9 Comparative Zn 2.6 a 5 0.36 0.58 Good 68.0 Example B-13 Ni19.4 Co 110.0 Comparative Zn 2.6 e 5 0.51 0.50 Good 68.2 Example B-14 Ni19.4 Co 109.2 Example B-1 Zn 13.2 e 5 1.50 1.03 Good 73.3 Ni 5.8 a:γ-Glycidoxypropyltrimethoxysilane b:γ-Methacryloxypropyltrimethoxysilane c: γ-Acryloxypropyltrimethoxysilaned: γ-Chloropropyltrimethoxysilane e: γ-Aminopropyltrimethoxysilane

As Table 6 shows, various rust proofing treatments were performed on theelectrodeposited copper foil of Example 3, and after electrolyticchromate treatment (using 1.0 g/L chromic acid solution), five types ofsilane coupling agent treatment of a to e in Table 6 were performed,respectively. The conditions for rust proofing treatment were asfollows:

-   -   Conditions of rust proofing treatment of Comparative Examples        B-1 to 5 (treated in the following order)

1. Zinc (Zn) rust proofing treatment Zn concentration 6.0 g/L Potassiumpyrophosphate 140 g/L pH 10.5 Liquid temperature 40° C. Current density1.25 A/dm² Treating time 12 seconds 2. Water washing treatment 3.Electrolytic chromate treatment CrO₃ concentration 1.0 g/L pH 12.0Liquid temperature 25° C. Current density 1.25 A/dm² Treating time 12seconds 4. Water washing treatment 5. Silane coupling agent treatment 6.Drying treatment 150° C.

-   -   Conditions of rust proofing treatment of Comparative Examples        B-6 and 7

Tin (Sn) rust proofing treatment Sn concentration 6.0 g/L Potassiumpyrophosphate 100 g/L pH 10.5 Liquid temperature 40° C. Current density0.75 A/dm² Treating time 12 seconds

After this Sn rust proofing treatment, treatments on and after No. 2 ofthe above-described B-1 to 5 were performed.

-   -   Conditions of rust proofing treatment of Comparative Examples        B-8 and 9

Nickel (Ni) rust proofing treatment Ni concentration 6.0 g/L Potassiumpyrophosphate 100 g/L pH 10.5 Liquid temperature 40° C. Current density0.5 A/dm² Treating time 12 seconds

After this Ni rust proofing treatment, treatments on and after No. 2 ofthe above-described B-1 to 5 were performed.

-   -   Conditions of rust proofing treatment of Comparative Examples        B-10 and 11

Cobalt (Co) rust proofing treatment Co concentration 3.0 g/L Potassiumpyrophosphate 100 g/L pH 10.5 Liquid temperature 40° C. Current density0.5 A/dm² Treating time 12 seconds

After this Co rust proofing treatment, treatments on and after No. 2 ofthe above-described B-1 to 5 were performed.

-   -   Conditions of rust proofing treatment of Comparative Examples        B-13 and 14

Zinc (Zn)-nickel (Ni)-cobalt (Co) ternary system rust proofing treatment

Zn concentration 0.25 g/L Ni concentration 3.0 g/L Co concentration 4.0g/L Potassium pyrophosphate 100 g/L pH 10.5 Liquid temperature 40° C.Current density 0.5 A/dm² Treating time 12 seconds

After this Zn—Ni—Co ternary rust proofing treatment, treatments on andafter No. 2 of the above-described B-1 to 5 were performed.

The conditions of rust proofing treatment of Comparative Example B-12and Example B-1 were the same as conditions in Table 2 of theabove-described first embodiment. The silane coupling treatment wasperformed by preparing solutions of various silane coupling agents of ato e (5 g/L). The surface roughness of the adhering surfaces of all theelectrodeposited copper foils, which were surface-treated as in Table 6,was 0.8 μm in Rz.

The evaluation of adhesion was performed after the above-describedsurface treatment, by applying a commercially available polyimidevarnish (Rikacoat SN-20 manufactured by New Japan Chemical Co., Ltd.) toeach electrodeposited copper foil and heated to form a laminated filmformed by laminating polyimide layers (insulating layers) of a thicknessof 40 μm, and by measuring each peel strength. The measurement of peelstrength was performed in accordance with JIS-C-6481 for the normalstate and after heat treatment at 150° C. for 50 hours. Blackeningevaluation was performed by observing the surface state of theinsulating layer that has emerged by alkali etching of the conductivelayer using an A Process vat solution (manufactured by Meltex Inc.).Since the optical transmittance was measured in the same method asdescribed above, the description thereof will be omitted.

As Table 6 shows, it was known that Example B-1 had a very high peelstrength, and had no practical problems. When Zn, Sn, Ni, or Co was usedalone for rust proofing treatment, or when the Zn—Ni—Co ternary rustproofing treatment was performed, it was found that a lower peelstrength was exhibited than a peel strength after the Zn—Ni binary rustproofing treatment even when the same silane coupling agent was used.Furthermore, it was confirmed that amino functional silane of the silanecoupling agent c tended to elevate peel strength compared to othersilane coupling agents (a, b, d, and e). Attainment of a higher peelstrength by this amino functional silane suggests, from the structuralformulas of respective silane coupling agents, that the relativebulkiness of silane chain in each structural formula may be involved.

INDUSTRIAL APPLICATION

According to the flexible printed wiring board of the present invention,as described above, since the optical transmittance of the insulatinglayer constituting the flexible printed wiring board becomes 50% ormore, the alignment when ICs are mounted can be performed accurately,and not only the adhesion of the conductive layer and the insulatinglayer is satisfactory, but also migration resistant characteristicsbecome highly excellent. Furthermore, since no nodular treatment isperformed on the electrodeposited copper foil that forms the conductivelayer, a flexible printed wiring board for fine-pitch COF can easily beformed.

1. A flexible printed wiring board for a chip on film (hereafterreferred to as COF), comprising an insulating layer and an etchedconductive layer, the conductive layer comprising an electrodepositedcopper foil having an adhering surface to which a rust-proofing layer isadhered, the rust-proofing layer located between the insulating layerand the conductive layer and comprising a nickel-zinc alloy, wherein theinsulating layer has an optical transmittance of 50% or more in regionswhere the conductive layer is etched, and wherein the surface roughness(Rz) of the adhering surface is 0.05 to 1.5 μm, and the adhering surfacehas a specular gloss of 250 or more when the incident angle is 60°. 2.The flexible printed wiring board for COF according to claim 1, whereinthe nickel-zinc alloy consists of 99 to 50 wt % nickel and 1 to 50 wt %zinc.
 3. The flexible printed wiring board for COF according to claim 1,wherein the rust-proofing layer is a nickel-zinc alloy layer having achromate layer formed thereon and a silane coupling agent adsorbed layerwhereon an amino functional silane coupling agent is adsorbed is formedon the surface of said rust-proofing layer.
 4. The flexible printedwiring board for COF according to claim 1, wherein the adhering surfaceof the electrodeposited copper foil is a glossy surface.